Causes of Surface Cracks in ASTM A588GrA Steel

When the ASTM A588GrA steel slab is heated at high temperature, the copper oxide remaining in the heating furnace is reduced to free copper at high temperature, and the molten copper atoms expand along the grain boundaries of the slab structure, weakening the force between grains.

The strength and melting point of copper are much lower than those of steel, and copper infiltrates and diffuses along the grain boundaries of the billet structure at high temperature. At the same time, since copper is more difficult to oxidize than iron, when the copper content in ASTM A588GrA steel is more than 0.2% (mass percentage), the slab is heated to 1100~1200 ℃, and the oxidizing gas reacts with the slab. With the continuous formation of iron oxide scale on the surface of the billet, the iron content of the surface layer of ASTM A588GrA steel gradually decreases, and the copper content increases relatively until it exceeds its solid solubility in iron.

Copper is enriched under the scale skin, forming a molten copper layer at high temperature and eroding the grain boundaries of the ASTM A588GrA steel slab structure, and gradually spreading along the grain boundaries, resulting in micro-cracks, similar to over-fired crack-like crack defects or densely distributed pitting surface defects.